Uterine fibroids are non-cancerous tumors that develop in the wall of uterus. Such fibroids occur in a large percentage of the female population with some studies indicating up to 40 percent of all women have fibroids. Uterine fibroids can grow over time to be several centimeters in diameter and symptoms can include menorrhagia, reproductive dysfunction, pelvic pressure and pain.
One current treatment of fibroids is hysteroscopic resection or myomectomy which involves transcervical access to the uterus with a hysteroscope together with insertion of a resecting instrument through a working channel in the hysteroscope. The resecting instrument may be a mechanical tissue cutter or an electrosurgical resection device such as an RF loop. Mechanical cutting devices are disclosed in U.S. Pat. Nos. 7,226,459; 6,032,673, 5,730,752 and U.S. Published Patent Appl. 2009/0270898. An electrosurgical resecting device is disclosed in U.S. Pat. No. 5,906,615.
In a myomectomy or hysteroscopic resection, the initial step of the procedure includes distention of the uterine cavity to create a working space for assisting viewing through the hysteroscope. In a relaxed state, the uterine cavity collapses with the uterine walls in contact with one another. A fluid management system is used to distend the uterus to provide a working space by means of a fluid being introduced through a passageway in the hysteroscope under sufficient pressure to expand or distend the uterine cavity. The fluid management system can be used for diagnostic or operative hysteroscopic procedures. Typically, saline solution is used to as a distention fluid. Fluid management systems typically use a controller which controls inflows and outflows of distention fluid to maintain a set pressure in the uterine cavity. The distention fluid pressure provides a benefit in the tamponade effect on vascularized tissue at the resection site. The distension fluid pressure typically exceeds the patient's mean arterial pressure, and thus the pressure can prevent leakage of arterial blood from the resection site into the uterine cavity. When such arterial blood leaks into the distension fluid, it can reduce the clarity of the visual field and make the procedure more difficult or cause suspension of the procedure. Thus, it is useful to maintain fluid pressure above the arterial pressure to provide a clear visual field.
One disadvantage of the use of distention fluids in hysteroscopic procedures is that it places women at risk for fluid overload from intravasation of distention fluid by the patient's venous system. Such intravasation can cause electrolyte imbalances with a potential for pulmonary edema and congestive heart failure. A typical fluid management system has fluid deficit monitoring capabilities wherein the volume of intravasated fluid is determined by calculating the difference between the fluid weight/volume introduced into the patient minus the weight/volume of fluid collected from the patient during the course of a procedure. A typical fluid management system includes a visual display of fluid deficit and a warning signal for an excessive fluid deficit.
The are several disadvantages related to the use of conventional weight-based fluid management systems. First, it is typically difficult to maintain a pre-set fluid pressure to distend the uterine cavity during a resection procedure because the cutting device suctions fluid through the device to draw tissue into a cutting window and thereafter suctions fluid and resected tissue through the device to collection reservoirs. Thus, suctioning fluid from the uterine cavity needs to be compensated for with corresponding fluid inflows into the cavity to maintain cavity distention. Typical weight-based fluid management systems have a pressure sensor that will activate the inflow pump to deliver distention fluid to the uterine cavity when intra-cavity pressure drops. However, use of the cutting device and associated suction may cause a very rapid drop in pressure resulting in collapse of the cavity before replacement inflows of distention fluid are sufficient to maintain distention of the cavity. A collapse of the cavity results in loss of visualization and would require the physician to interrupt the procedure. The drop in intra-cavity distention fluid pressure also may result in leakage of greater amounts of blood into the cavity which further causes a loss of visualization.
One promising approach for fluid management in hysteroscopic and other endoscopic procedures is the recirculation and filtration of the saline electrolytic distension fluid. In order for such a saline filtration and recirculation system to be safe and effective, the filter and flow control system would need to provide a filtrate that does not include lysed red blood cells and that has an unaltered electrolyte concentration. Further, the filtrate should not cause any effect on a coagulation pathway of a patient or cause activation of an inflammation-related immune response in the patient. For these reasons, it would be desirable to provide filtering systems and methods and flow control systems for preventing hemolysis and for controlling electrolyte fluid management in hysteroscopic and other procedures which maintain the electrolytic concentrations in the saline and provide a filtrate that does not activate a coagulation response or an immune response in the event of intrvasation of the filtrate. At least some of these objectives will be met by the inventions described below.